#define _CRT_SECURE_NO_WARNINGS 1
#include<iostream>
using namespace std;

int tribonacci(int n)
{
    if (n == 0)  return 0;
    if (n == 1 || n == 2)  return 1;
    int a = 0, b = 1, c = 1;
    int d;
    for (int i = 3; i <= n; i++)
    {
        d = a + b + c;
        a = b;
        b = c;
        c = d;
    }
    return d;
}

int main()
{
    int n = 3;
    int ret = tribonacci(n);
    cout << ret << endl;
    return 0;
}